The invention relates to a composition useful in the repair and/or restoration of dental lesions as well as repair and/or restoration of other calcium and calcium phosphorus containing parts of living organisms.
Remineralization of dentin enamel and bone utilizing calcium phosphate materials has been the subject material of intense experimentation and research. Nonetheless, there has remained a need for improved remineralization techniques and materials.
Dental cements are materials traditionally used under permanent restorations and, with the exception of polycarboxylate and glass ionomer cements, do not adhere to tooth structure. Their function and effectiveness lies mainly in insulation of the living tooth tissue (the pulp and the dentin) against thermal and bacterial effects from the oral cavity. While many of these materials have thus been effective base cements, they can do little to promote any healing effects to the diseased tooth tissues.
Other cements, so-called pulp-capping materials, promote the repair mechanism of dentin in the case of a perforated pulp. However, these materials have low strength and do not adhere to dentinal tissue. Clinically, the failure of pulp capping is directly related to the inability of Ca(OH)2, for example, to provide a long-term seal against microleakage.
Newer technology has led to the development of a number of cement-type materials with various desirable properties, e.g., biocompatibility; ease of use due to the ability of being cured on command with light-curing; and higher strength; as for instance, in resin-reinforced glass ionomer cements. Many materials used today lack at least one of these properties, leaving the dentist with less than optimal choices for the caries treatment. There is a need for a strong material that serves not only as a base and pulp-capping material, but will also induce reparative mechanisms of carious dentin and/or enamel.
None of the cements that are currently in use can act in this dual manner as a pulp-capping/basing cement while simultaneously promoting the repair of mineral deficient tooth structure through the precipitation of tooth-like minerals.
For example, Antonucci et al., U.S. Pat. No. 4,832,745, describes a polymeric amorphous calcium phosphate composition to be used as a mineralizing composition for skeletal tissue, which contains a mixture of an unsaturated monomer systems and a particulate mineralizing agent. The composition contains approximately 40% amorphous calcium phosphate (ACP) mixed with approximately 60% monomers. While the ACP-based formulation has a reasonable potential for mineralizing carious enamel (no data on dentin remineralization have been provided), the monomer formulation cannot adhesively bond to hard tooth tissue nor does it contain or would be able to release any fluoride.
Since Antonucci""s invention contains 40% calcium phosphate minerals, such cement consists mostly of resin. High organic fraction resins typically do not provide the necessary strength required from a base cement. Also, a cement of such composition may not be suited as a base cement, since the coefficient of thermal expansion due to the high organic mass, is considerably high.
Hino et al., U.S. Pat. No. 5,814,681, describes a restorative composition for hard tissue containing calcium phosphates and polymerizable monomers. Each paste contains calcium phosphates as fillers and a monomer mixture comprised of 2 monomers, one of which is a mono-, di-, or tri-ethyleneglycol dimethacrylate or polypropyleneglycol dimethacrylate, (monomer of formula (1)). The second monomer (monomer of formula (2)) is an ethoxylated bisphenol A dimethacrylate. Hino claims that the restorative composition can be used as a bone cement, as well as a filler for the defect part of the bone, a bone prosthesis, or an artificial bone. However, Hino""s composition would not provide adhesive properties.
Hino discloses that the combination of monomers (1) and (2) contains 40-65% by weight monomer of formula (1) and that the inorganic content of pastes A and B should be 75-85% by weight. Hino""s use of calcium phosphates requires silanization treatment with methacryloxypropyltrimeth(eth)oxysilane. Although Hino mentions the use of secondary calcium phosphate and tetracalcium phosphate, the temperature used in the disclosed heat treatment to silanate the calcium phosphate fillers, would in the case of secondary calcium phosphate lead to the formation of pyrophosphate. Pyrophosphates are known to inhibit the formation of hydroxyapatite and would therefore be contraindicated for use as bone filling repair material where bone in growth is required to ultimately heal the defect. Also, Hino""s use of hydroxyapatite powder as fillers would lead to a minimal release of calcium ions.
The cement formulation described by Waller, U.S. Pat. No. 4,746,686, for a visible light-activated hydroxyapatite-containing cavity liner is capable of leaching fluoride ions and contains a small proportion of a hydrophilic monomer. Apart from using hydroxyapatite as fillers, the cement mixture reported by Waller has a considerably low strength and a neutral pH.
Wang, U.S. Pat. No. 4,813,876 describes a cavity liner, that is photo-polymerizable and is based on calcium hydroxide. Walton, U.S. Pat. No. 4,886,843 describes a very similar composition containing calcium hydroxide or their precursors and ethylenically unsaturated, polymerizable compounds having a salicylate group. The latter two patents describe resin-based cements that could be used for pulp-capping; however, the calcium hydroxide-based cements lack a phosphate component and therefore would not lead to any remineralization.
A great number of highly biocompatible cements using calcium phosphates as fillers have been described. (Brown et al., U.S. Pat. Nos. 4,612,053; 4,518,430; RE33,221; Chow et al., U.S. Pat. No. 5,695,729; Winston et al., U.S. Pat. Nos. 5,603,922; 5,833,957; 5,614,175; 5,817,296; Ison, U.S. Pat. Nos. 5,846,312; 5,496,399; Constantz, U.S. Pat. Nos. 5,129,905; 5,782,971; Imura et al., U.S. Pat. Nos. 5,569,490 and 5,652,016.) The majority are water based cements. Brown and Chow describe use of fillers in water-based self setting calcium phosphate cements consisting of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrate or dihydrate. The TTCP must have a Ca to P ratio of 2 or less.
Other prior art water based cements with reinforcing additives lack the advantage of being light-cured or do not have readily available PO4 ions, that in combination with Ca ions could lead to the formation of the biornimetic hydroxyapatite. Cements that incorporate hydroxyapatite or other calcium phosphate powders and (poly)carboxylic acids are described by Adachi, U.S. Pat. No. 4,684,673; Liu, U.S. Pat. No. 5,218,035 and Bajpai, U.S. Pat. No. 4,668,295. Jochum and Gasser, U.S. Pat. No. 4,542,172 describe a lining and pulp-capping mixture based on calcium hydroxide, salicylic acid esters and poly-vinylbutyral as a binder. Aoki et al., U.S. Pat. No. 4,452,167, describes a dental cement composition, comprising hydroxyapatite, and acrylic acid/itaconic acid copolymers as the hardener.
The invention is directed to a pulp-capping and base/lining cement formulation comprising the combination of two pastes or a liquid and a powder. Each paste contains a polymerizable monomer, a calcium phosphate powder, and other additives. The monomers provide an adhesive resin component and a reinforcing base resin component. The calcium phosphate powders are tetracalcium phosphate and dicalcium phosphate. A preferred embodiment provides a paste composed of a polymerizable base monomer and tetracalcium phosphate. Other additives include catalysts able to initiate polymerization of the resin components and a fluoride-releasing compound. After the two pastes or liquid and powder are combined, the cement contains dispersed in unsaturated monomers calcium phosphate fillers, which then form hydroxyapatite when exposed to moisture. The monomers will harden into a polymer network.
The hardened cement consists of hydroxyapatite, some residual non-apatitic calcium phosphates, and an organic matrix. The hydroxyapatite may be present in quantities of 0 to 100 wt %, typically between 10 and 75 wt %. During and after setting, the calcium phosphate resin cement has a basic pit provides freely available calcium and phosphate ions, and provides slow and continuous release of fluoride. The cement also has adhesive properties, which is unique for a material that can be used for indirect or direct pulp-capping procedures.
The pulp-capping and base/lining cement formulation can be used for reconstruction of diseased or lost tooth structure or as a prophylactic treatment. Because of its high strength, the cement is useful as a basing material, and because of its adhesive properties, the cement will be able to seal the perforated pulp against bacterial invasion. In addition, it is believed that the cement will stimulate the formation of reparative dentin because of its basic pH during and after setting and will also promote remineralization of mineral deficient tissues.
The invention is directed to a two-part resin composition. When the two parts are combined, a mixture results of an acidic resin, tetra calcium phosphate powder, dicalcium phosphate powder, and water to provide two interpenetrating, reacting phasesxe2x80x94a polymeric phase and a mineral phase. The pH of the mixture when initially mixed is at least about 11, but after about 24 hours, the pH of the mixture is about 8 to 12, preferably about 8 to 11, more preferably about 10. The higher pH allows the reacted mixture to be utilized for dental repair.
The invention is also directed to a method of dental repair comprising applying the rapidly curing mixture as a tooth repair or filling material to provide adequate strength and properties which stimulate natural regenerative repair of the damaged pulped region.
Numerous other features, objects and advantages of the invention will become apparent from the following detailed description.